1. Field of the Invention
This invention relates to improved polymeric materials and, more particularly, to polymer alloys finding particular use as fire-retardant and flame-resistant materials, and in membranes useful in a variety of separation processes.
2. The Prior Art
The blending of polymer materials is a well established technique for improving certain properties of the polymeric system with a minimum sacrifice of its other desirable characteristics. For example, phosphorus-containing polymers have attracted considerable interest in recent years for their fire-retardant characteristics, and blends of such materials with other thermoplastic polymers have been described as possessing other improved properties while retaining the desired flame-retardant characteristics of the base polymeric material. Kraft et al. U.S. Pat. Nos. 3,725,509 and 3,819,770 may be noted in this respect.
Polymer blends of the type disclosed in the aforesaid Kraft et al. patents do not form "true" blends or "polymer alloys," i.e., blends in which the mixing of the several polymeric components is so intimate that they cannot be separated by solvents which dissolve only individual components. Only very few polymer mixtures have heretofore been recognized as forming such polymer alloys. See Encyclopedia of Polymer Science and Technology, Vol. 10, page 694 (1969). The formation of such polymer alloys is of particular interest for fiber or film applications.
Polymer alloys based on sulfonated polystyrene and copolymers of acrylonitrile have been used as ion-exchange membranes, whereas polymer alloys based on polyvinylpyrrolidone and polyisocyanates have been tested as membranes in desalination processes. Blends of polystyrene and poly(phenylene oxide) have also been described as forming polymer alloys. See J.Appl. Polym.Sci., 16, 461-471 (1972) and J.Polymer Sci.Symposium No. 41, 23-32 (1973).
It is among the objects of the present invention to provide improved polymer alloys useful both for their improved fire-retardant and flame-resistant characteristics, and for their superior permeability characteristics facilitating application as polymeric membranes for the separation of various solvent species.